Heavy-intensity aerobic exercise affects the isokinetic torque and functional but not conventional hamstrings:quadriceps ratios

Running exercises are frequently related to muscular injuries, which may be a result of muscular imbalance. The present study aimed to verify the effects of heavy-intensity continuous running exercise on the functional and conventional hamstrings:quadriceps ratios, and also in the knee flexors and extensors EMG activity in active non-athletic individuals. Sixteen active males performed maximal isokinetic concentric and eccentric knee flexions and extensions at 60° s^?1 and 180° s^?1. In another session, the same procedure was conducted after a continuous running exercise at 95% onset of blood lactate accumulation. Torque and electromyographic ratios were calculated from peak torque and integrated electromyographic activity (knee flexor and extensors). Creatine kinase was measured before and 24 h after running exercise. Eccentric torque (knee flexion and extension) decreased significantly after running only at 180° s^?1 (p < 0.05). No differences were found for the conventional torque ratios (p > 0.05), however, the functional torque ratios at 180° s^?1 decreased significantly after running (p < 0.05). No effects on the electromyographic activity and electromyographic ratios were found (p > 0.05). Creatine kinase increased slightly 24 h after running (p < 0.05). Heavy-intensity continuous running exercise decreased knee flexor and extensor eccentric torque, and functional torque ratios under fast velocities (180° s^?1), probably as result of peripheral fatigue.     

The eccentric,concentric strength relationship of the hamstring muscles in chronic low back pain

ObjectiveThe objective of this study was to measure hamstring muscle eccentric and concentric strength in individuals with and without low back pain (LBP). Two composite scores for the relative balance of eccentric to concentric strength at the different movement velocities were calculated (the DEC and SEC), to determine whether or not self perceived pain, disability, or fear avoidance measures were associated with hamstring strength characteristics.DesignCross-sectional repeated measures design.SettingUniversity laboratory.ParticipantsFifteen individuals with chronic LBP and 15 matched controls.Main outcome measuresIsokinetic eccentric and concentric strength at 30° s^?1 and 120° s^?1_. Composite scores (DEC and SEC) based on peak torque were calculated to evaluate the relationship between the different muscle actions across the test velocities. Self report measures included the Oswestry disability index, general health and well being, fear avoidance, and pain.ResultsEccentric/concentric strength ratio at 30° s^?1 was higher for the LBP group (F(1,58) = 4.81, p = 0.032). The SEC was also higher for the LBP (F(1,58) = 5.97, p = 0.018). Fear avoidance beliefs and mental well-being were significantly associated with the SEC only in the LBP group (adjusted r² = 0.26, (F(2,27) = 5.8, p = .008). For the control group both the DEC and SEC were associated with self report measures. Matched differences between groups’ for the SEC were best explained by fear avoidance beliefs about work (adjusted r² = 0.12, F(1,28) = 5.1, p = 0.03).ConclusionReduced concentric relative to eccentric strength is best identified by the SEC. The SEC was significantly associated with impaired self report measures of fear avoidance and mental well being in individuals with LBP. Differences between groups for the SEC were best explained by fear avoidance beliefs about work.     

Purification,kinetic and thermodynamic characterization of soluble acid invertase from sugarcane (Saccharum officinarum L.)

We report for the first time kinetic and thermodynamic properties of soluble acid invertase (SAI) of sugarcane (Saccharum officinarum L.) salt sensitive local cultivar CP 77-400 (CP-77). The SAI was purified to apparent homogeneity on FPLC system. The crude enzyme was about 13 fold purified and recovery of SAI was 35%. The invertase was monomeric in nature and its native molecular mass on gel filtration and subunit mass on SDS-PAGE was 28 kDa. SAI was highly acidic having an optimum pH lower than 2. The acidic limb was missing. Proton transfer (donation and receiving) during catalysis was controlled by the basic limb having a pKa of 2.4. Carboxyl groups were involved in proton transfer during catalysis. The kinetic constants for sucrose hydrolysis by SAI were determined to be: k_m = 55 mg ml^?1, k_cat = 21 s^?1, k_cat/k_m = 0.38, while the thermodynamic parameters were: ΔH* = 52.6 kJ mol^?1, ΔG* = 71.2 kJ mol^?1, ΔS* = ?57 J mol^?1 K^?1, ΔG*_E–S = 10.8 kJ mol^?1 and ΔG*_E–T = 2.6 kJ mol^?1. The kinetics and thermodynamics of irreversible thermal denaturation at various temperatures 53–63 °C were also determined. The half -life of SAI at 53 and 63 °C was 112 and 10 min, respectively. At 55 °C, surprisingly the half -life increased to twice that at 53 °C. ΔG*, ΔH* and ΔS* of irreversible thermal stability of SAI at 55 °C were 107.7 kJ mol^?1, 276.04 kJ mol^?1 and 513 J mol^?1K^?1, respectively.     

Characterization of a HAP–phytase from a thermophilic mould Sporotrichum thermophile

The phytase of Sporotrichum thermophile was purified to homogeneity using acetone precipitation followed by ion-exchange and gel-filtration column chromatography. The purified phytase is a homopentamer with a molecular mass of ～456 kDa and pI of 4.9. It is a glycoprotein with about 14% carbohydrate, and optimally active at pH 5.0 and 60 °C with a T_1/2 of 16 h at 60 °C and 1.5 h at 80 °C. The activation energy of the enzyme reaction is 48.6 KJ mol^?1 with a temperature quotient of 1.66, and it displayed broad substrate specificity. Mg²⁺ exhibited a slight stimulatory effect on the enzyme activity, while it was markedly inhibited by 2,3-butanedione suggesting a possible role of arginine in its catalysis. The chaotropic agents such as guanidinium hydrochloride, urea and potassium iodide strongly inhibited phytase activity. Inorganic phosphate inhibited enzyme activity beyond 3 mM. The maximum hydrolysis rate (V_max) and apparent Michaelis–Menten constant (K_m) for sodium phytate were 83 nmol mg^?1 s^?1 and 0.156 mM, respectively. The catalytic turnover number (K_cat) and catalytic efficiency (K_cat/K_m) of phytase were 37.8 s^?1 and 2.4 × 10⁵ M^?1 s^?1, respectively. Based on the N-terminal and MALDI–LC–MS/MS identified amino acid sequences of the peptides, the enzyme did not show a significant homology with the known phytases.     

Kinematic and electromyographic analysis of the Nordic Hamstring Exercise

The Nordic Hamstring Exercise (NHE) has been introduced as a training tool to improve the efficiency of eccentric hamstring muscle contraction. The aim of this study was to perform a biomechanical analysis of the NHE. Eighteen participants (20.4 ± 1.9 years) performed two sets of five repetitions each of the NHE and maximal eccentric voluntary contraction (MEVC) of the knee flexors on an isokinetic dynamometer whilst knee angular displacement and electrical activity (EMG) of biceps femoris were measured. EMG was on average higher during the NHE (134.3% of the MEVC). During the forward fall of the NHE, the angle at which a sharp increase in downward velocity occurred varied between 47.9 and 80.5 deg, while the peak knee angular velocity (pVelocity) varied between 47.7 and 132.8 deg s^?1. A significant negative correlation was found between pVelocity and peak EMG (r = ?0.62, p < 0.01) and EMG at 45 deg (r = ?0.75, p < 0.01) expressed as a percentage of peak MEVC EMG. Some of the variables analyzed exhibited good to excellent levels of intra- and inter-session reliability. This type of analysis could be used to indirectly monitor the level of eccentric strength of the hamstring muscles while performing the NHE and potentially any training- or injury-related changes.     

Muscle architecture variations along the human semitendinosus and biceps femoris (long head) length

The purpose of this study was to examine whether muscle architecture of the long head of biceps femoris (BF) and semitendinosus (ST) muscles varies along their length. The ST and BF muscles were dissected and removed from their origins in eight cadaveric specimens (age range 67.8–73.4 years). One-way analysis of variance designs were used to compare fascicle length (FL), pennation angle (PA) and muscle thickness (MT) between proximal, mid-belly and distal positions. Tendon and muscle length properties were also quantified. For the BF muscle, one-way analysis of variance tests showed a higher PA (23.96 ± 3.82°) and FL (7.12 ± 0.48 cm) proximally than distal positions (PA = 17.78 ± 1.95° and FL = 6.35 ± 0.89 cm, respectively). For the ST, there was a significantly (p < 0.05) lower PA (8.81 ± 1.22°) and FL (13.10 ± 1.54 cm) proximally than distally (PA = 14.69 ± 1.09° and FL = 15.49 ± 2.30 cm, respectively). Muscle thickness significantly increased from distal to more proximal positions (p < 0.05). These data suggest that the ST and BF architecture is not uniform and that measurement of these parameters largely depends on the measurement site. Modeling these muscles by assuming a uniform architecture along muscle length may yield less accurate representation of human hamstring muscle function.     

Fire service instructor's undergarment choice to reduce Interleukin-6 and minimise physiological and perceptual strain

Fire Service Instructors frequently experience high levels of physiological and perceptual strain during live fire exposures. Instructors are also at risk of cardiovascular illnesses, with cardiac death being the greatest cause of fire fighter death. Current practice for UK instructors is to select undergarment type based on personal preference, between a boiler suit (BOILER) and a wicking base layer (WBL). Research suggests that shorts and t-shirt (SHORTS) may also be a beneficial alternative undergarment choice. The UK South East Fire Service requested an investigation to identify if undergarment selection can lessen the strain experienced by instructors, and reduce the acute inflammatory response to fire exposures. Eight males completed three 45 min sessions in a heat chamber (49.5±1.4 °C and 16.9±4.3% RH) whilst performing intermittent walking. At the end of heat exposure change in heart rate was not effected by garment type (p=0.061, ηp²=0.373). Change in rectal temperature was different between garments (p=0.009, η_p²=0.271), with trends suggesting that BOILER resulted in a greater change (1.03±0.60 °C) than SHORTS (0.76±0.37 °C, p=0.589, d=0.21) and WBL (0.72±0.33 °C, p=0.545, d=0.25). Interleukin-6 post exposure was greater for BOILER (6.96±0.28 pg mL⁻¹) than both SHORTS (6.59±0.30 pg mL⁻¹, p=0.043, d=0.42) and WBL (6.45±0.43 pg mL⁻¹, p=0.031, d=0.51). Overall, undergarment type had little impact on physiological or perceptual strain. However, wearing WBL or SHORTS may reduce the inflammatory response, and consequently decrease the risk of cardiovascular events.     

Isolation and properties of β-xylosidase from Aspergillus niger GS1 using corn pericarp upon solid state fermentation

There is growing interest in developing high-yield and low-cost production of xylanolytic enzymes for industrial applications using agroindustrial byproducts. A native strain of Aspergillus niger GS1 was used to produce β-xylosidase (EC 3.2.1.37) on solid state fermentation using corn pericarp (CP) with innovative alkaline electrolyzed water (AEW) pretreatment at room temperature. β-xylosidase was purified by ammonium sulfate fractionation followed by anion exchange and hydrophobic interaction chromatographies. β-Xylosidase showed a molecular weight of 111 kDa, isoelectric point of 5.35 and specific activity of 386.7 U (mg protein)^?1, using p-nitrophenyl-β-d-xylopyranoside as substrate, at pH 5 and 60 °C, and optimal activity at pH 4.5. Optimal temperature was 65 °C, showing full activity after 1 h at 60 °C. Activity was reduced by 1 mM β-mercaptoethanol (55.6 ± 0.1%), and enhanced by 1 mM SDS (11.0 ± 0.03%). K_m and V_max were 6.1 ± 0.9 mM and 1364 ± 105 U (mg protein)^?1, respectively, whereas k_cat was 5.1 s^?1. A predominant α-helix (41%) was determined from circular dichroism on β-xylosidase, while thermal transition profiles produced a T_m of 54.1 ± 5.8 °C, enthalpy change for unfolding of 67.4 ± 6.7 kJ/mol, and onset temperature of 37 °C. Pre-treatment of CP using AEW is an ecologically friendly alternative to chemical and heat treatments for the production of relatively high levels of β-xylosidase.     

Glucose isomerase production on a xylan-based medium by Bacillus thermoantarcticus

Effects of medium components on intracellular glucose isomerase (GI) production were investigated by Bacillus thermoantarcticus. The highest GI activity was obtained as 1630 U dm^?3 in the medium containing (g dm^?3): 10.6, birchwood-xylan; 5.6, yeast extract; 5.9 (NH₄)₂SO₄ at T = 55 °C in 33 cm^?3 shake-flasks. When birchwood-xylan was replaced with oat spelt- or beechwood-xylan, GI activity decreased to 1372 and 1308 U dm^?3, respectively. Effects of pH at uncontrolled-pH (pH_UC = 6.0) and controlled-pH (pH_C = 6.0) operations, and oxygen transfer at the air inlet rate of 0.5 vvm and agitation rates of 300, 500 and 700 min^?1, were investigated in 3.0 dm³ bioreactor system with 1.65 dm³ working volume in the designed medium. The highest GI activity was attained at 500 min^?1, 0.5 vvm, pH_UC = 6 as 1840 U dm^?3 where cell concentration was 2.3 g dm^?3. The use of agricultural waste xylan, as the carbon source resulted in concomitant production of xylanase and GI. The highest xylanase activity was attained as 9300 U dm^?3 at 500 min^?1 and 0.5 vvm. K_La varied between 0.008–0.033 s^?1 whereas the highest oxygen uptake rate was 0.002 mmol dm^?3 s^?1. Initially biochemical reaction limitations were effective; thereafter, mass transfer resistances became more effective.     

Electromyographic patterns of lower limb muscles during apprehensive gait in younger and older female adults

ObjectiveInvestigate the influence of apprehensive gait on activation and cocontraction of lower limb muscles of younger and older female adults.MethodsData of 17 younger (21.47 ± 2.06 yr) and 18 older women (65.33 ± 3.14 yr) were considered for this study. Participants walked on the treadmill at two different conditions: normal gait and apprehensive gait. The surface electromyographic signals (EMG) were recorded during both conditions on: rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), tibialis anterior (TA), gastrocnemius lateralis (GL), and soleus (SO).ResultsApprehensive gait promoted greater activation of thigh muscles than normal gait (F = 5.34 and p = 0.007, for significant main effect of condition; RF, p = 0.002; VM, p < 0.001; VL, p = 0.003; and BF, p = 0.001). Older adults had greater cocontraction of knee and ankle stabilizer muscles than younger women (F = 4.05 and p = 0.019, for significant main effect of groups; VM/BF, p = 0.010; TA/GL, p = 0.007; and TA/SO, p = 0.002).ConclusionApprehensive gait promoted greater activation of thigh muscles and older adults had greater cocontraction of knee and ankle stabilizer muscles. Thus, apprehensive gait may leads to increased percentage of neuromuscular capacity, which is associated with greater cocontraction and contribute to the onset of fatigue and increased risk of falling in older people.     

Characterization of a novel laccase from the isolated Coltricia perennis and its application to detoxification of biomass

A highly efficient laccase-producing fungus was isolated from soil and identified as Coltricia perennis SKU0322 by its morphology and by comparison of its internal transcribed spacer (ITS) rDNA gene sequence. Extracellular laccase (Cplac) from C. perennis was purified to homogeneity by anion-exchange and gel filtration chromatography. Cplac is a monomeric glycoprotein with 12% carbohydrate content and a molecular mass of 66 kDa determined by polyacrylamide-gel electrophoresis. Ultraviolet-visible absorption spectroscopy observed type 1 and type 3 copper signals from Cplac. The enzyme acted optimally at pH 3–4 and 75 °C. Its optimal activity was with 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS), it also oxidized various lignin-related phenols. The enzyme was characterized as a multi-copper blue laccase by its substrate specificity and internal amino acid sequence. It showed a higher catalytic efficiency towards ABTS (k_cat/K_m = 18.5 s^?1 μM^?1) and 2,6-dimethoxyphenol (k_cat/K_m = 13.9 s^?1 μM^?1) than any other reported laccase. Its high stability and catalytic efficiency suggest its suitability for industrial applications: it detoxified phenolic compounds in acid-pretreated rice straw and enhanced saccharification yield.     

Influence of erythrocyte aggregation on radial migration of platelet-sized spherical particles in shear flow

Blood platelets when activated are involved in the mechanisms of hemostasis and thrombosis, and their migration toward injured vascular endothelium necessitates interaction with red blood cells (RBCs). Rheology co-factors such as a high hematocrit and a high shear rate are known to promote platelet mass transport toward the vessel wall. Hemodynamic conditions promoting RBC aggregation may also favor platelet migration, particularly in the venous system at low shear rates. The aim of this study was to confirm experimentally the impact of RBC aggregation on platelet-sized micro particle migration in a Couette flow apparatus. Biotin coated micro particles were mixed with saline or blood with different aggregation tendencies, at two shear rates of 2 and 10 s⁻¹ and three hematocrits ranging from 20 to 60%. Streptavidin membranes were respectively positioned on the Couette static and rotating cylinders upon which the number of adhered fluorescent particles was quantified. The platelet-sized particle adhesion on both walls was progressively enhanced by increasing the hematocrit (p < 0.001), reducing the shear rate (p < 0.001), and rising the aggregation of RBCs (p < 0.001). Particle count was minimum on the stationary cylinder when suspended in saline at 2 s⁻¹ (57 ± 33), and maximum on the rotating cylinder at 60% hematocrit, 2 s⁻¹ and the maximum dextran-induced RBC aggregation (2840 ± 152). This fundamental study is confirming recent hypotheses on the role of RBC aggregation on venous thrombosis, and may guide molecular imaging protocols requiring injecting active labeled micro particles in the venous flow system to probe human diseases.     

Purification of recombinant mandelate racemase: Improved catalytic activity

Mandelate racemase (MR, E.C. 5.1.2.2) from Pseudomonas putida catalyzes the Mg²⁺-dependent 1,1-proton transfer that interconverts the enantiomers of mandelate and has been studied extensively as a model for understanding how enzymes catalyze the deprotonation of carbon acid substrates with relatively high pK_a values. Purification of recombinant MR as a fusion protein with an N-terminal hexahistidine tag using immobilized-nickel ion affinity chromatography and elution with a linear gradient of EDTA revealed three enzyme species (mrI, mrII, and mrIII). While mrIII was catalytically inactive, both mrI and mrII catalyzed the racemization of (S)-mandelate with turnover numbers (k_cat) of 190 ± 22 and 940 ± 24 s^?1, respectively. Circular dichroism analysis suggested that mrIII was a partially unfolded or misfolded form of the enzyme. Replacement of the N-terminal hexahistidine tag by a StrepII-tag appeared to ameliorate the folding problem yielding a single enzyme species with a turnover number of 1124 ± 43 s^?1. The MR fusion protein bearing an N-terminal StrepII-tag and a C-terminal decahistidine tag also exhibited reduced turnover (k_cat = 472 ± 37 s^?1). These results highlight a potential problem that may be encountered when producing fusion enzymes bearing a polyhistidine tag: soluble, active enzyme may be obtained but care must be taken to ensure that it is free of minor misfolded forms that can alter the apparent activity of the enzyme.     

Nitrate and phosphate uptake kinetics of the harmful diatom Eucampia zodiacus Ehrenberg,a causative organism in the bleaching of aquacultured Porphyra thalli

The diatom Eucampia zodiacus Ehrenberg is a harmful diatom which indirectly causes bleaching of aquacultured Nori (Porphyra thalli) through competitive utilization of nutrients during bloom events. In the present study, we experimentally investigated the nitrate (N) and phosphate (P) uptake kinetics of E. zodiacus, Harima-Nada strain. Maximum uptake rates (ρ_max), which were obtained by short-term experiments, were 0.777 and 0.916 pmol cell^?1 h^?1 for nitrate and 0.244 and 0.550 pmol cell^?1 h^?1 for phosphate at 9 and 20 °C, respectively. The half-saturation constants for uptake (K_s) were 2.59 and 2.92 μM N and 1.83 and 4.85 μM P at 9 and 20 °C, respectively. Although the maximum specific uptake rate (V_max; V_max = ρ_max/Q₀, Q₀; minimum cell quota) and V_max/K_s for nitrate at 9 °C are about 1/2 of those obtained at the optimum temperature (20 °C), they are still higher than those obtained for many other phytoplankton at their optimum temperature conditions for uptake. These results suggest that E. zodiacus utilizes nitrogen efficiently at low water temperature, and it is one of the important factors causing the serious damage to Porphyra thalli by bleaching due of this species. For phosphate, the K_s values of E. zodiacus were higher than those reported for other species; the V_max and V_max/K_s values were much lower than those of other diatoms such as Skeletonema costatum (Greville) Cleve. These results suggest that E. zodiacus is disadvantaged compared to other diatom species during competitive utilization of phosphate.     

Multi-channel electromyography during maximal isometric and dynamic contractions

Motor unit behavior differs between contraction types at submaximal contraction levels, however is challenging to study during maximal voluntary contractions (MVCs). With multi-channel surface electromyography (sEMG), mean physiological characteristics of the active motor units can be extracted. Two 8-electrode sEMG arrays were attached on biceps brachii muscle (one on each head) to examine behavior of sEMG variables during isometric, eccentric and concentric MVCs of elbow flexors in 36 volunteers.On average, isometric (364 ± 88 N) and eccentric (353 ± 74 N) MVCs were higher than concentric (290 ± 73 N) MVC (p < 0.001). Mean muscle fiber conduction velocity (CV) was highest during eccentric MVC (4.42 ± 0.49 m/s) than concentric (4.25 ± 0.49 m/s, p < 0.01) and isometric (4.14 ± 0.45 m/s, p < 0.001) MVCs. Furthermore, eccentric MVC showed lower sEMG amplitude at the largest elbow joint angles (120–170°) and higher CV at the smallest (70–150°) elbow joint angles (p < 0.05–0.001) than concentric MVC.The differences in CV and sEMG amplitude between the MVCs suggest that the control strategy of motor units differs between the contraction types during MVCs, and is dependent on the muscle length between the dynamic MVCs.     

Intramuscular fine-wire electromyography during cycling: Repeatability,normalisation and a comparison to surface electromyography

This study investigated (a) the feasibility and repeatability of intramuscular fine-wire electromyographic (fEMG) recordings from leg muscles during the repetitive, high-velocity cycling movement, (b) the influence of amplitude normalization technique on repeatability and statistical sensitivity, (c) the influence of test-retest interval duration on repeatability, and (d) differences between fEMG and surface EMG (sEMG) recordings of cycling. EMG activity of leg muscles was recorded using surface and fine-wire electrodes during one (n = 12, to investigate statistical sensitivity and compare sEMG and fEMG) or two sessions (T1 and T2, 5–20 days apart, n = 10, to investigate repeatability). fEMG recordings were feasible and there was high repeatability of fEMG recordings normalised to maximum measured EMG amplitude (MAX); mean coefficients of multiple correlation (CMC) ranged from .83 ± .13 to .88 ± .07. Data normalised to maximal (MVC) or submaximal contractions (sMVC) were less repeatable (p < .01). Statistical sensitivity was also greatest for data normalised to MAX (p < .01). Repeatability of fEMG increased with greater test-retest intervals (p < .01). The global pattern of muscle recruitment was consistent between sEMG and fEMG but sEMG recordings were characterized by additional myoelectric content. These findings support and guide the use of fEMG techniques to investigate leg muscle recruitment during cycling.     

Diminished sub-maximal quadriceps force control in anterior cruciate ligament reconstructed patients is related to quadriceps and hamstring muscle dyskinesia

The aim of this study was to determine the effects of anterior cruciate ligament reconstruction (ACLR) on sub-maximal quadriceps force control with respect to quadriceps and hamstring muscle activity. Thirty ACLR individuals together with 30 healthy individuals participated. With real-time visual feedback of muscle force output and electromyographic electrodes attached to the quadriceps and hamstring muscles, subjects performed an isometric knee extension task where they increased and decreased their muscle force output at 0.128 Hz within a range of 5–30% maximum voluntary capacity. The ACLR group completed the task with more error and increased medial hamstring and vastus medialis activation (p < 0.05). Moderate negative correlations (p < 0.05) were observed between quadriceps force control and medial (Spearman’s rho = −0.448, p = 0.022) and lateral (Spearman’s rho = −0.401, p = 0.034) hamstring activation in the ACLR group. Diminished quadriceps sub-maximal force control in ACLR subjects was reflective of medial quadriceps and hamstring dyskinesia (i.e., altered muscle activity patterns and coordination deficits). Within the ACLR group however, augmented hamstring co-activation was associated with better quadriceps force control. Future studies should explore the convergent validity of quadriceps force control in ACLR patients.     

Muscle fatigue and metabolic responses following three different antagonist pre-load resistance exercises

PurposePreload of antagonist muscles can be achieved by reciprocal actions (RAs) or by opposing muscle actions. However, evidence concerning neuromuscular and fatigue responses are scarce.ObjectiveTo compare the effects of different knee flexor (KF) preload methods on knee extension (KE) vastus medialis muscle fatigue, based on EMG-spectral index (FI), load range (LR), total work (TW), blood lactate (LAC) and biceps femoris co-activation (BFc) during resistance exercise.MethodsTwenty-four healthy men (23.5 ± 3.6 yrs) performed three antagonist pre-load isokinetic exercises (4 sets, 10 repetitions, 60° s^?1, 1 min rest between sets): RA (KF contraction immediately followed by KE); Superset (SS; one KF set immediately followed by one KE set); Multiple Set (MS; four KF sets followed by four KE sets).ResultsTotal work was significantly greater in RA. There was no significant decrease in LR between sets in RA. The BFc did not differ between protocols (p = 0.063). However, RA presented greater biceps femoriscoactivation. The FI was greater during SS compared to RA and MS (p < 0.05). The SS had greater LAC when compared to MS and RA (p = 0.005 and p = 0.007, respectively).ConclusionIt is suggested that the RA protocol is more neuromuscular and metabolic efficient during the performance of knee extension resistance exercise.     

Oxidation of the diphosphoinositol polyphosphate phosphohydrolase-like Nudix hydrolase Aps from Drosophila melanogaster induces thermolability—A possible regulatory switch?

Unlike mammalian cells, Drosophila melanogaster contains only a single member of the diphosphoinositol polyphosphate phosphohydrolase subfamily of the Nudix hydrolases, suggesting that functional specialisation has not occurred in this organism. In order to evaluate its function, Aps was cloned and characterized. It hydrolyses a range of (di)nucleoside polyphosphates, the most efficient being guanosine 5′-tetraphosphate (K_m = 11 μM, k_cat = 0.79 s^?1). However, it shows a 5-fold preference for the hydrolysis of diphosphoinositol pentakisphosphate (PP-InsP₅, K_m = 0.07 μM, k_cat = 0.024 s^?1). Assayed at 26 °C, Aps had an alkaline pH optimum and required a divalent ion: Mg²⁺ (10–20 mM) or Mn²⁺ (1 mM) were preferred for nucleotide hydrolysis and Mg²⁺ (0.5–1 mM) or Co²⁺ (1–100 μM) for PP-InsP₅ hydrolysis. GFP-fusions showed that Aps was predominantly cytoplasmic, with some nuclear localization. In the absence of dithiothreitol Aps was heat labile, rapidly losing activity even at 36 °C, while in the presence of dithiothreitol, Aps was heat stable, surviving for 5 min at 76 °C. Heat lability was restored by H₂O₂ and mass spectrometric analysis suggested that this was due to reversible dimerisation involving two inter-molecular disulphides between Cys23 and Cys25. Aps expression was highest in embryos and declined throughout development. The ratio of PP-InsP₅ to inositol hexakisphosphate also decreased throughout development, with the highest level of PP-InsP₅ found in embryos. These data suggest that the redox state of Aps may play a role in controlling its activity by altering its stability, something that could be important for regulating PP-InsP₅ during development.     

Kinematics of cross-country sit skiing during a Paralympic race

The study had three purposes: to verify a hypothesized speed decrease during the 15 km cross-country sit skiing (CCSS) race; documenting this possible fatigue effect (speed decrease), to evaluate changes among the four laps in kinematics parameters (cycle speed, cycle duration, cycle length, duty cycle (percentage ratio between pushing and total cycle duration), pole inclination, trunk inclination and shoulder–hand distance); to compare the kinematics parameters in cross-country sit skiers of different level. Video recordings were carried out during the 2006 Turin Winter Paralympic Games with two conventional digital video-cameras positioned on a flat and an uphill (8.3°) track, respectively. Better performing skiers (G1) had significantly higher speeds than worse performers (G2) both in the flat (6.54 ± 0.13 vs. 5.89 ± 0.50 m s^?1 and 5.55 ± 0.14 vs. 4.62 ± 0.22 m s^?1 in the first and last lap, respectively) and in the uphill track (3.67 ± 0.45 vs. 3.05 ± 0.59 m s^?1 and 3.20 ± 0.36 vs. 2.26 ± 0.36 m s^?1 in the first and last lap, respectively). The G1 athletes were able to maintain the high-speed better than the G2 over the entire race. Significant differences in cycle length and duty cycle between groups would be justified by the higher physical fitness of G1 skiers.